JUST four months ago it seemed that Donald Trump was unassailable in his bid to be re-elected for a second term. His America First platform secured him the presidency in 2016 because it spoke to blue-collar workers who had seen entire cities turned to urban praries as the US lost manufacturing jobs to China. And he was delivering.

Now those gains have been wiped out by coronavirus. A record 20.5 million jobs vanished in April alone, sending unemployment rates hurtling towards the Great Depression figures of the 1930s. It's no surprise, then, that his Democrat rival in November's election, Obama's former Vice-President Joe Biden, is experiencing a surge in the polls. But what would a Biden presidency mean for the rest of the world? For Britain, the first risk is once again being pushed "to the back of the queue" when it comes to a trade deal.

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Covid-19's economic fall-out is already likely to make the US-UK FTA process more complicated, with both governments under even more pressure to bring the best deal home. But while Trump continues to prioritise a quick deal, Biden has already stated that Brexit diminished Britain's importance to Washington by removing an influential voice in the EU, and might favour rekindling a deal with Brussels first.

Another risk is dilution of the Special Relationship as Biden ponders US dealings with a PM whom he considers, rightly or wrongly, to be made in Trump's mould.

A return of classical liberalism will bring other changes, starting with the overturning of his predecessor's executive orders. Trump's "maximum pressure" policy on Iran (signs of success include regime funding to terror groups such as Hezbollah down 40 percent) would be reversed as economic sanctions are lifted, and the US rejoins what some thought Obama's foreign policy masterstroke, the Joint Comprehensive Plan of Action - the flawed deal aiming to curb nuclear missile ambitions.

The US would rejoin the Paris Climate Accord, which Trump is leaving in November, and rekindle the Trans-Pacific Partnership (TPP) which seeks an EU-style single market for 12 Pacific-bordering countries.

Four months ago it seemed that Donald Trump was unassailable in his bid to be re-elected (Image: Getty)

But those who think a Biden presidency means "Obama 2.0" do not recognise the altered state of the world we now live in.

China's actions over coronavirus have hardened world opinion against Beijing, which accepts it faces a level of global criticism not seen sinceTiananmen Square. But the crisis, to quote the Henry Jackson Society's eloquent founder James Rogers, "has merely acted like a flash of lightning at night which reveals the landscape". While Trump's (anti-) China policy is robust, Obama had already begun to recognise the strategic and economic threat posed by Beijing, and so does Biden.

But there are differences. Trump's approach is to meet this head-on, trusting that his policies (the US represents a quarter of the world's GDP) will ripple on to First World economies and conglomerates. If reelected, we may see more radical policies from a President unrestrained by elections.

Biden, whom even supporters say has "never been accused of having political imagination", will renurture Pacific alliances aiming for a united front. There will also be a rebuilding of relationships with Nato allies, strained over the past four years despite mainland Europe now hosting the most US troops since the ColdWar. But if European members feel relief, it will over style, not substance. Obama began to press Europe on defence spending; this will continue under Biden.

Donald Trump's America First platform secured him the presidency in 2016 (Image: Getty)

With Russia inevitably mired in election disinformation campaigns, any winner would be expected to keep sanctions.And Biden would not have long to jumpstart arms control talks with Moscow. They expire in February and are stalled because Trump wants to include China.

Yet a Biden victory isn't a done deal: Americans vote on domestic issues. Trump's populism was a symptom of a festering scepticism against globalism and a liberal elite. Ironically, the crisis that threatens Trump may be his saviour.

Flagship Biden policies such as extending Medicare (the health insurance plan nearing bankruptcy) and launching the Green New Deal may seem too costly in the worst economic crisis in 70 years.

National polls show Biden leading 51 points to 46, yet in 15 "battleground" states Trump leads 52 to 45. When asked if the economic crash will hurt Trump, 57 percent say no.Trump risks a second Covid-19 wave with efforts to kickstart the economy.

But while his popularity with the over-65s has dipped, there is support from younger voters keen to get back to work. The question may be: China has caused the US economy to crash - who do you trust to build it up again quickly?